After four decades of mind-boggling spending for weapons and 15 years of go-nowhere negotiations, the superpowers are making hopeful noises about reducing military forces in Europe.

It goes beyond the peace rhetoric President Reagan and Soviet leader Mikhail S. Gorbachev have voiced at their summits in Geneva, Reykjavik and Washington.Moscow has conceded for the first time that it does indeed have an advantage over the West in some military categories. Red Army leaders hint they may no longer feel the need for such superiority.

"It appears that in 1988 both East and West are ready for a new beginning," says Thomas J. Hirschfeld, who spent 1979 to 1982 as a U.S. representative to the multilateral Mutual and Balanced Force Reduction talks that have dragged on inconclusively since 1973.

Reagan was said to be prepared to touch on the need for conventional disarmament, in a speech in Helsinki, Finland, on his way to the May 29-June 2 summit, but there's no telling what he and Gorbachev might do on the issue.

U.S. officials are bracing for the possibility that Gorbachev will suggest that the two superpowers meet this fall to discuss cutting their ground forces in Europe by as much as 25 percent.

One official raised the possibility that Gorbachev might wait until after the summit to announce a unilateral withdrawal of 50,000 to 70,000 troops. Another official said 100,000 troops could be pulled back.

After Secretary of State George P. Shultz attended a pre-summit planning session with the Soviets earlier this month there was little talk of conventional weaponry being a major topic at the summit. Optimism on the issue focused on the possibility of a mid-July agreement on a mandate for lower level negotiations, the Conventional Stability Talks.

Before they begin such talks, the Western participants want further Eastern European compliance with human rights accords signed in 1975. Still, U.S. officials are hoping the problems can be settled in time for the CST conference to begin in October.

"Of course, the CST talks will not reach agreement overnight and, indeed, it will be well into the next U.S. president's term before they produce results," said former Capitol Hill staff member Thomas Longstreth, in a study for the Federation of American Scientists.

"With time and patience, the logjam can be broken and a new era of stability in Europe achieved," Longstreth wrote.

Since the end of World War II, Red Army forces in Europe have been dominated by huge armies of men, tanks and artillery suitable for attack. By Pentagon estimates, the Soviets have 230 divisions, compared with 121 for NATO; an edge of 52,000-to-24,250 in main battle tanks and a 42,000-to-18,350 edge in artillery.

The Soviets have said they need such forces to keep the military balance. In a speech last year, however, Gorbachev acknowledged that "asymmetries" exist in the force comparisons and said the goal of each side should be "reasonable sufficiency," rather than superiority.